1. Field of the Invention
This invention relates to novel laminated materials comprising a layer of metal foil overcoated with two layers of cured polymeric material. More specifically, this invention relates to heat-sealable laminates that are especially useful as packaging materials, for example for the packaging of photographic processing chemicals, which comprise a layer of metal foil, an outer heat-sealable layer of a radiation-cured and heat-fused polymeric composition, and a radiation-cured chemically-resistant polymeric interlayer between the foil and the outer layer.
2. Description of the Prior Art
Laminates which comprise a layer of metal foil bonded to a layer of thermoplastic polymer are well-known materials. As described by Marans and Addy in an article entitled "Film Lamination by Radiation-Induced Polymerization of Acrylic Acid," Journal of Applied Polymer Science, Vol. 9, pages 3661-3680, 1965, they can be prepared by using techniques such as heat plus pressure, adhesives, electric discharges, flaming, and further polymerization or crosslinking of prepolymers. The specific procedure described in detail by Marans and Addy involves the use of radiation-induced explosive polymerization of acrylic acid to form a discrete poly(acrylic acid) layer which serves as an interlayer between two films, such as a metal foil and a thermoplastic polymer film.
Prior methods of forming laminates of metal foils and thermoplastic films suffer from serious disadvantages which significantly restrict the usefulness of the resulting materials. For example, it is a common problem for the material to undergo delamination in use, especially when subjected to conditions of high temperature and high humidity. Moreover, even if delamination does not occur, the laminate may be adversely affected by the heat used in heat-sealing operations, or it may be lacking in ability to act as an effective barrier to oxygen and thereby be unable to adequately protect chemicals packaged therein from unwanted oxidation, or it may be subject to attack by common chemicals such as alkaline agents. Materials used in bonding the metal foil to the thermoplastic film may be effective as bonding agents but the bonding layer formed therefrom may be incapable of protecting the metal foil from attack by chemicals. Packaging materials used with sensitive chemicals, for example, many of the chemicals used in photographic processing, must possess a combination of characteristics such as strength, imperviousness to oxygen and moisture, and resistance to chemical attack, and laminates previously known have been lacking in one or more of these characteristics or have been incapable of being heat-sealed by common heat-sealing methods and, accordingly, have not found widespread use for this purpose.
Heat-sealable laminates prepared by the method described in copending patent application Ser. No. 694,758, which is referred to hereinabove, overcome many of the disadvantages of prior art laminates and represent an important advance in the technology of laminated packaging materials. However, there is a need for alternative manufacturing techniques which are more easily adapted to low cost mass production than the method of application Ser. No. 694,758 and it is toward the accomplishment of this objective that the present invention is directed.